Accurately understanding and quantitatively analyzing the stress state and evolution law of engineering rock mass (facilities) is a basis for determining construction plans and preventing and controlling sudden engineering disasters in mining, petroleum and civil engineering. For example, in construction projects such as urban traffic tunnels, railway and highway tunnels, submarine traffic tunnels and pipelines, coal mine roadways, water conveyance tunnels and the like, the stress distribution and evolution law of the engineering rock mass (facilities) are required to be obtained for the design and stability analysis of the above objects. In general, although the engineering structure is in a three-dimensional stress state, for the engineering structure having the size of the third direction much larger than that of the other two directions, the stress state thereof can generally be abstracted and simplified into a plane strain problem.
Laboratory experiments, especially similar simulation experiments, have been widely used in the research of plane strain problems. Compared with theoretical analyses, stress analyses of research objects with relatively complex geometric shapes can be performed through similar simulation experiments; compared with numerical calculations, controversial operation processes, such as mesh division and algorithm selection, are not required in the similar simulation experiments; compared with field measurement, similar simulation experiments have the advantages of low cost, repeatability, and controllable research variables. Therefore, similar simulation experiments are of great value for the stress analysis of engineering rock mass (facilities) with complex mechanisms, numerous influencing factors and different working conditions.
The plane strain problem is studied in the similar simulation experiment, and rigid metal plates are widely used to constrain the deformation in the normal directions of two surfaces of the experimental model, so that the experimental model can satisfy the conditions of the plane strain problem. However, since the rigid metal plate is not transparent, the change processes of the physical characteristics on the surface of or inside the similar experimental model cannot be displayed in this kind of solutions, which makes it impossible for the researchers to visually observe the stress, deformation and failure phenomena of the experimental model. Moreover, as a branch of the similar simulation experiments, two-dimensional photoelastic similar simulation experiments often employ transmissive optical systems, if rigid metal plates are mounted at two sides of the plane model, it is difficult to carry out this type of photoelastic experiments.
Baffles made of rigid transparent materials provide a solution to the above problems, which have been researched in related patents and literatures in recent years. In summary, according to the conventional technical solutions of baffles made of rigid transparent materials, bolts are generally used to fix the rigid transparent baffles, and the experimental model is located between two rigid transparent baffles, so that the deformation of the experimental model in one direction is constrained by the rigid transparent baffles. However, the above solution has the following disadvantages. First, it is difficult to tighten multiple bolts at the same time, and it is also difficult to ensure that each bolt provides an exactly equal tightening force to the rigid transparent baffles; with the above solution, additional stress of the experimental model are easily generated; although the difference of the tightening force has relatively small effect on the similar simulation model made of soil and sand material, it has a great influence on the similar simulation model made of the material with the stress birefringence effect. Second, the mounting steps of bolts, the rigid transparent baffles and the experimental model are complicated, and it takes a long time to adjust the pre-tightening force of each bolt. Third, according to the technical solutions of the disclosed patents, the constraint methods based on the magnetism rigid transparent baffle plates are rarely used for assembling the rigid transparent baffle plates and the experimental model.